One of the final stages in the fabrication of integrated circuits on semiconductor wafers is testing and sorting of the functionality of the individual semiconductor chips, the dies. The purpose of testing the dies is to determine if the dies function as they were designed for; i.e., whether the dies produce intended outputs for given inputs. Once functionality is established, the dies are sorted for operating frequency, i.e., the dies are ranked in terms of how fast each die operates. Due to the variations in processing steps, different dies function at different speeds.
There are a variety of techniques employed for testing the dies. One key factor in determining the method of testing the dies is the complexity of the device design. The number of input and output (I/O) pads present on a die is often indicative of the complexity of the design, wherein a higher number of I/O pads is attributed to higher design complexity.
A die with a low number of I/O pads arranged in a linear array can be tested using probe stations where individual probe leads are brought into mechanical contact with each I/O pad. Typically, the number of pads in the linear array is less than, or on the order of, about 25. The individual probe leads provide power and input signals to the input pads and measures output signals from the output pads. For a die with a mid-range number of I/O pads, customized probe cards with many probe leads can be generated wherein the probe leads are arranged to correspond to each I/O pad on the mid-range die. The customized probe cards may also be wired and connected to a tester to provide power and input signals and analyze output signals from the die. For a die with a high number of I/O pads, i.e., those having hundreds to thousands of I/O pads typically in an aerial array, customized probe cards connecting the die to a tester is impractical and expensive, and in some instances impossible. An economical alternative is needed.
Where testing or measuring of the die with customized probe cards is impractical for a die with a high number of I/O pads, it is often advantageous to use packaging mounts, e.g., ceramic or organic modules in which the die to be tested may be mounted, in order to facilitate testing of the die. In this way, wiring from the I/O pads of the die under test to tester compatible pin of the packaging mount is readily available. The temporary wiring, or electrical connections of the I/O pads of the die to the packaging mounts is preferred over permanent packaging of the die since the costly process of forming the permanent packaging may be avoided should the die under test be found defective.
Interposers are devices commonly used in manufacturing for forming temporary electronic connections for the purpose of probing of a semiconductor die with a high number of I/O pads. FIG. 1 is a schematic view of a system in which an interposer 100 provides an electrical connection between a tester 110 and a semiconductor wafer 120. Such interposers offer a convenient way of testing electronic components, such as semiconductor wafers, without requiring a permanent electrical connection, such as solder bonds, between the electronic components and a tester. A permanent electrical connection, such as a die packaging, would have to be dismantled or discarded were the tested component deemed defective. Thus, such interposers often provide a method of economically determining the functionality of semiconductor wafers or semiconductor dies in the semiconductor industry.
Interposers currently in use for testing of semiconductor wafers may be electrolytic plated interposers designed to probe rigid, non-even surfaces such as those commonly associated with ceramic packaging modules. Flexible interposers, which may probe non-rigid surfaces, that are currently available are difficult and cost-prohibitive to fabricate, and requires unusual processing techniques that are not readily practiced. Currently available interposers tend to target rigid substrates, such as silicon dies or silicon substrates.
Thus, current interposers also fail to facilitate probing of flexible substrates that are becoming more common with the use of organic semiconductor materials and flexible substrate materials.
Therefore, there exists a need for a flexible interposer structure for probing flexible, non-rigid semiconductor dies and methods of fabricating the same.
There also exists a need for a more economical interposer structure for probing rigid surfaces and methods of fabricating the same.